Packaging and storage— Preserve in collapsible ophthalmic ointment tubes.

USP Reference standards á11ñ— USP Bacitracin Zinc RS.USP Polymyxin B Sulfate RS.

Thin-layer chromatographic identification test á201BNPñ: meets the requirements.

Sterility á71ñ— It meets the requirements when tested as directed for Membrane Filtrationunder Test for Sterility of the Product to be Examined.

Minimum fill á755ñ: meets the requirements.

Water,Method Iá921ñ: not more than 0.5%,20mLof a mixture of toluene and methanol (7:3)being used in place of methanol in the titration vessel.

Metal particles á751ñ: meets the requirements.

Assay for bacitracin— Proceed with Ophthalmic Ointment as directed in the Assayunder Bacitracin Zinc Ointment.

Assay for polymyxin B— Proceed as directed for polymyxin Bunder Antibiotics—Microbial Assays á81ñ,using an accurately weighed portion of Ophthalmic Ointment shaken with about 50mLof ether in a separator and extracted with four 20-mLportions of Buffer No.6.Combine the aqueous extracts,and dilute with Buffer No.6to an appropriate volume to obtain a stock solution.Dilute this stock solution quantitatively and stepwise with Buffer No.6to obtain a Test Dilutionhaving a concentration assumed to be equal to the median dose level of the Standard.

Expert Committee:(PA7)Pharmaceutical Analysis 7

USP28–NF23Page 217

Phone Number:1-301-816-8335